Almost all Samsung phones cheaper than other sites on Zopper + Additional 300 off by signing up on app

I have compared with Delhi prices. Did check prices are similar in Bangalore but Zopper offers different prices in different cities.
Following are few examples prices are cheaper on all samsung phones i saw and also quicker delivery (they claim 24 hour delivery but my experience has been more towards 48 hours with once even delivery within 3 hours of placing order).

Samsung J2 – 7484 – 300 Signup = 7184
https://m.zopper.com/pd/9...67

Amazon 7590 http://www.amazon.in/dp/B015J...8/
Flipkart 7590 http://www.flipkart.com/samsung-galaxy-j2/p/itm...

Samsung J7 – 13770 – 300 Signup = 13440
https://m.zopper.com/pd/9...99

Amazon – 14249 http://www.amazon.in/Samsung-Galaxy-J7-SM-J700F...
Flipkart – 15990 http://www.flipkart.com/samsung-galaxy-j7-6-new...

Samsung S7 -47390 -300 Signup = 47090
https://m.zopper.com/pd/9...50

Amazon 50,990 http://www.amazon.in/Samsung-Galaxy-S7-SM-G930F...
Flipkart 48900 http://www.flipkart.com/samsung-galaxy-s7/p/itm...